Studies on learning in infants show that in infancy every month of life represents a new level of learning. The functional state of the central nervous system can be influenced by physiological factors which cause fluctuating changes in functions important for learning. Once a stimulus becomes a conditioned signal, it acquires strong power in influencing an infant's behavior. More is known about the relative value of different reinforcing unconditioned stimuli than about the relative value of conditioning stimuli. Further research is needed on the development of central mechanisms responsible for the processing of sensory input and for the structuring and integration of information. It is likely that preverbal forms of information interaction and integration will become the center of increased research attention. In studies of postnatal development, the physiological and psychological disciplines merge. (MS)